In order to maintain prolonged sealing performance in a mechanical seal, it is necessary to achieve the contradictory conditions of airtightness and lubricity. In recent years especially, there has been an even greater demand for lower friction in order to reduce mechanical loss while also preventing leakage of a sealed fluid, in part because of environmental measures. Friction can be reduced by achieving a “fluid-lubrication state,” in which rotation creates dynamic pressure between sealing faces and the faces slide with a liquid film interposed therebetween. However, in such a case, positive pressure occurs between the sealing faces, and therefore the fluid flows out from the positive pressure portion to the outside of the sealing face. This outward flow of fluid qualifies as leakage in cases of sealing.
The present applicants, having made improvements to the manner in which a sealed fluid is introduced between sealing faces and is held there, have previously filed for a patent for the invention of a mechanical seal sliding member for obtaining stable and favorable lubrication performance, i.e., for causing sealing faces where a stationary sliding member and a rotating sliding member face each other to rotate and slide in a relative fashion and for sealing in a sealed fluid present on one side, in the radial direction, of the sealing faces rotating and sliding in a relative fashion in order to lower the coefficient of friction without creating excess leakage. In this configuration, there are formed, spaced apart on the sealing faces, a plurality of grating parts where a plurality of rectilinear irregularities in parallel with each other are formed at a predetermined pitch in a predetermined section, the rectilinear irregularities of the plurality of grating parts being formed so that the direction of the irregularities is sloped at a predetermined angle with respect to the sliding direction of the sealing faces (“Prior Art 1;” see Patent Citation 1).
Also known is an invention of a low-friction sealing face having a grating-like periodic structure formed in a plurality of discrete regions of a mirror surface portion forming a solid material surface, all of the regions being sectioned with the entire periphery thereof surrounded by the mirror surface portion and the mirror surface portion being one continuous surface, the objective of the invention being to provide a sealing face structure having excellent reciprocating sliding properties in a stopped state (“Prior Art 2;” see Patent Citation 2).
Further known is an invention of a sealing face structure in which a sealing face of a first member and a sealing face of a second member slide in a relative fashion in the presence of a lubricant. In this configuration, a plurality of grating parts comprising a plurality of irregularities are formed along the sliding direction on the sealing face of the first member and/or the second member and the direction of a periodic structure of grating parts adjacent along the sliding direction is symmetrical with respect to the sliding direction. An objective of this invention is to provide a sealing face structure whereby low friction can be achieved and familiar steps can be shortened (“Prior Art 3;” see Patent Citation 3).
However, as is illustrated in FIG. 14, Prior Art 1 does not state that the grating parts 50, being formed in a range between radii R2 and R3 of the sealing face 51 of an inner radius R1 and an outer radius R4, communicate with the sealed fluid side, and thus the grating parts 50 are not intended to actively keep catching the sealed fluid at the start-up of the mechanical seal, nor is the amount of sealed fluid caught by the grating parts 50 adequate after start-up. The amount of sealed fluid caught by the grating parts during start-up and after start-up will also have been limited, because the grating parts 50 are formed substantially flush with the sealing face 51.
Also, in Prior Art 2 as illustrated in FIG. 15, the plurality of grating-like periodic structure parts 60 are sectioned, with the entire periphery thereof surrounded by the mirror surface portion 61, and do not communicate with the outside of the zones of the mirror surface portion 61; therefore, because the grating-like periodic structure parts 60 are covered by the opposing sliding members in the case of application to a mechanical seal and do not communicate with the sealed fluid side, the grating-like periodic structure parts 60 will be unable to catch the sealed fluid present outside of the zones of the mirror surface portion 61 during start-up of the mechanical seal, nor can the amount of sealed fluid caught by the grating-like periodic structure parts 60 be adequate after start-up. Further, when the grating-like periodic structure parts 60 are formed at a point deeper than the mirror surface portion 61, although the amount of oil film that can be held increases, there is a decline in the efficacy of lateral leakage prevention by the periodic structure parts 60 during sliding, indicating that the grating-like periodic structure parts cannot be too deep.
In summary, Prior Art 2 makes no implication of use as a mechanical seal, and even with hypothetical use as a mechanical seal, discloses no technical idea whereby the sealed fluid would be actively caught by the grating-like periodic structure parts 60 during start-up of the mechanical seal and would be prevented from leaking out to the atmosphere side.
Prior Art 3, as illustrated in FIG. 16A, is a bearing or other sealing face structure in which a sealing face of a disc body 70 and a sealing face of a ring body 71 slide in a relative fashion in the presence of a lubricant. As illustrated in FIG. 16B, there are formed along the sliding direction on the sealing face 72 of the disc body 70 a plurality of grating parts 73a, 73b which are sectioned with the entire periphery thereof surrounded by the sealing face 72 and comprise a plurality of irregularities. As illustrated in FIG. 16C, the directions of periodic structures of grating parts 73a, 73b that are adjacent in the sliding direction are rendered symmetrical with respect to the sliding direction. However, the manner of application to any sealing face other than a bearing is not disclosed; even with hypothetical application to a mechanical seal, there is no indication that the grating parts 73a, 73b of the sealing face 72 of the disc body 70 communicate with the sealed fluid side. Therefore, no disclosure is made of a technical idea whereby the grating parts 73a, 73b would actively catch the sealed fluid during start-up and after start-up of the mechanical seal. Additionally, since the grating parts 73a, 73b are formed substantially flush with the sealing face 72, a problem emerges in that the grating parts 73a, 73b are unable to catch the sealed fluid, and in that the sealing faces cannot be adequately lubricated during start-up and after start-up.